Almost seven decades after one of the deadliest battles in the Pacific theater, Leon Cooper, an 89-year-old veteran of World War II, returned to the small Pacific island of Tarawa, where he fought against Japanese soldiers, with a new mission: to clean up the historic site by collecting tons of garbage and rescuing military debris there.

But Cooper also was shocked to find there the human remains of several American soldiers still listed as missing in action. More than 1,000 U.S. Marines died and almost 3,000 were wounded in 1943 during a three-day assault to take control of Tarawa Island. The carnage still haunts Cooper, and he's waging a new battle.

"For more than three years," says Cooper, "I've been trying to get our government to do something about the desecration that has happened to the beaches that so many Americans died in defense of our country."

Steven C. Barber's new documentary, Return to Tarawa, follows Cooper to meetings with local officials and experts to get help with the cleanup operation.

Tarawa is so small that there is no place to bury trash. So Cooper has proposed that the island set garbage bins and collection centers along the beaches and recycle garbage. But it's not just the garbage: Live munitions are still strewn on the beach.

The most shocking find there is human remains. In the film, Mark Noah, a military historian, says hundreds of U.S. Marines are buried in the island's sands.

"There is 1,106 people lost at the end of the war," he says. "When the Army came to dig up these people and take them to the States, only 392 were dug up and brought back to the States."

Barber says it's unlikely they will be returned.

"The bottom line is, it's a very expensive process to bring these men home. It was seven decades ago. We're in the middle of a war right now. Nobody really cares, except there are still people alive who want these people to come home."

Cooper won't give up the fight, but time is running out until Tarawa sinks under the ocean.

"A couple of the islands in the 12-, 13-island archipelago are now beneath the ocean, and it's only a matter of time, maybe a dozen years or 20 or 30, before the entire island group will be called the new Atlantis, because there won't be any Tarawa any more," says the persevering octagenarian.

There are also fewer and fewer World War II veterans, like Leon Cooper, to give voice to their fallen comrades.